IP 1/35 



PHYSIOLOGICAL AGE AND 
SCHOOL ENTRANCE 



BY 

ARTHUR K. BEIK 
Clark University 



A DLSSERTATION SUBMITTED TO THE FACULTY OF 
CLARK UNIVERSITY, WORCESTER, MASS., IN PARTIAL 
FULFILLMENT OF THE REQUIREMENTS FOR THE 
DEGREE OF DOCTOR OF PHILOSOPHY, AND ACCEPTED 
ON THE RECOMMENDATION OF WILLIAM H. BURNHAM 



Reprinted from the Pedagogical Seminary 
September, 1913, Vol. XX, pp. 277-321 



PHYSIOLOGICAL AGE AND 
SCHOOL ENTRANCE 



BY 

ARTHUR K. BEIK 

Clark University 



A DISSERTATION SUBMITTED TO THE FACULTY OF 
CLARK UNIVERSITY, WORCESTER, MASS.. IN PARTIAL 
FULFILLMENT OF THE REQUIREMENTS FOR THE 
DEGREE OF DOCTOR OF PHILOSOPHY, AND ACCEPTED 
ON THE RECOMMENDATION OF WILLIAM H. BURNHAM 



Reprinted from the Pedagogical Seminary 
September, 1913, Vol. XX, pp. 277-321 



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Tb« University 
Uf 23 1811 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE^ 



By Arthur K. Beik, Clark University 



Introduction 

Child study has recognized in a general way alternating, 
or at least differentiated, periods of development, roughly 
classified according to predominant characteristics, physical 
and mental, and located with reference to the age of the 
child in years. Infancy is the term usually applied to the 
first year or years of life. Following infancy there comes 
the period of childhood, pretty sharply marked off at the 
later limit by the characteristics accompanying the attainment 
of pubescence. 

The period of childhood is again variously divided by the 
different authors, the location of the division points depend- 
ing upon the characteristics chosen as division marks. Be- 
cause of the grouping of some important factors about those 
years at which school is usually begun, it is becoming more 
general to designate this as a natural division point, or per- 
haps better, nodal period, of development. The time preced- 
ing this nodal period is referred to as " earlier childhood," 
while the time from this to the appearance of pubescence is 
referred to as " later childhood." Later childhood, then, be- 

^ Pres. G. Stanley Hall suggested the field in which to work out 
this thesis. The suggestions, advice and helpful criticism received 
from Dr. W. H. Burnham made its completion possible. For the 
helpful assistance from both these persons the writer wishes to 
acknowledge his indebtedness. He wishes also to express his thanks 
to those who assisted in the collection of material, among whom 
should be mentioned especially Dr. Theodate L. Smith and the library 
staff. 



278 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

gins approximately at the time of entrance to the graded 
school and continues up to, or until a short time after, the 
completion of the graded school work, and might well be 
characterized as " the age of the grades." 

The fact that it does so nearly coincide with the grade 
school years makes later childhood a most important period 
from the view points of child study and pedagogy. It is a 
period deserving of the closest study, especially as regards 
the child's development and his fitness to succeed in the tasks 
and cope with the new situations presented in the school 
environment. 

Following a brief characterization of the developmental 
features at the close of this later childhood period, it is our 
intention to take up in this paper a somewhat more detailed 
discussion of those developmental features that group them- 
selves about its beginning. It is our purpose to collect and 
condense available facts and data from the many investiga- 
tions that have dealt with particular phases of development 
in these early years, to relate them in so far as is possible, 
and to suggest something of their significance. 

What we have chosen to call the later limit of childhood 
is marked by those special phases of development that accom- 
pany the attainment of pubescence. It would be useless, for 
our purpose, to attempt a detailed description of these, though 
it may be worth while to mention a few of the more important 
points to which we may wish to refer later. 

Very prominent among the physical changes characteristic 
of the pubescent period is that of growth, both in height and 
weight. Growth in height shows a remarkable acceleration, 
extending over several years. The average time for girls is 
from the tenth or eleventh to the thirteenth or fourteenth 
year, while for boys it runs from about the eleventh or twelfth 
to the fifteenth or sixteenth years. Most curves show a simi- 
lar acceleration in weight following a little later, and occur- 
ring also a little earlier in girls than in boys. Both height 
and weight continue to increase for some time after this rapid 
acceleration, but at a slower and more uniform rate, so that 
boys and girls may be said to have almost reached adult size 
at the close of the rapid pubertal weight increase. 

Closely related to these phenomena of general growth, 
occur rapid growth of certain parts and organs, rapid changes 
in body proportions, remarkable additions in muscular power, 
change in quality and increase in quantity of possible mental 
achievement, and, perhaps most important of all, the attain- 
ment of pubescence. 

Dr. Crampton, e. g., would seem to give the factor of 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 279 

pubescence a place of prime importance, since he makes it the 
basis of grading for " physiological age " during this period 
(26). 

Data with regard to time of eruption of the teeth seem to 
indicate a close relationship of dentition to the general stage 
of advancement of development. From tabulations of the 
number of canines and molars present, Crampton finds a 
definite correlation of tooth appearance and weight and of 
tooth appearance and height (26). The more extended in- 
vestigations of dentition are of interest in this connection 
also. Boas and Wissler (11), Berten (8), and Rose {'j']^ 
all found that the eruption of the teeth was earlier, on the 
average, for girls than for boys. Recalling the fact of earlier 
pubescence of girls, the suggestion of a relationship between 
pubescence and dentition, or perhaps better, the relationship 
of both dentition and pubescence to the general stage of 
advancement in development, is strong. There is a problem 
here worthy of further investigation. More knowledge of 
the relationship of advancement of dentition at this time to 
other factors of development ought to be very valuable. 

Studies of the skeletal development, as worked out by 
Rotch (80), Pryor (70) and others, while not showing cor- 
relations for ossification of any particular part of the skeleton 
with pubescence, show in a general way a greater rapidity 
in girls at this stage of life. Great variability in degree of 
rapidity is also shown, especially by the work of Rotch and 
Smith (81) and also by that of Pryor indicated above. 

Variability in the time of these developmental phenomena 
is everywhere evident. Tabulations of growth all show that 
the acceleration extends over several years. Variability is 
fully as great in dentition, as indicated by the tabulations for 
time of tooth eruption. Time of appearance of pubescence 
is also extremely variable. Crampton found this factor ap- 
pearing in boys from 12.75 to 16.25 years of age. 

These main facts concerning the developmental phenomena 
prominent at the pubescent period are sufficient to indicate 
that the actual limitation of childhood is not to be referred to 
a mere temporal reckoning of the length of life, but rather 
to development. They indicate also that this limit does not 
coincide with a definitely marked " time line," but rather 
constitutes a broad " time zone " within which the transition 
from later childhood over to the earlier stages of the ado- 
lescent period is accomplished. Within this zone, the varia- 
bility is sufficiently great, as has been pointed out by Dr. 
Crampton, Rotch and Smith, Pryor and others, to render grad- 
ing on the basis of chronological basis alone inade^^juate. 



280 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

Finally, this stage of development is reached by girls earlier 
than by boys, as has been indicated by almost every study of 
development having to do with this period of life. 

While the close of later childhood is thus pretty clearly 
marked off by prominent developmental features, there is not 
at its beginning such a clear cut and astounding transition. 
Those factors which may be used as marks of development 
are much harder to distinguish, and therefore to correlate. 
There is available, however, a considerable body of facts that 
may assist us in the solution of one or two of the most im- 
portant problems that have to do with this period, and in the 
statement of some other problems that need solution. 

Among the important problems are these two : ( i ) Is 
there, at the age of five or six or seven years, evidence of a 
transition or nodality of development comparable in any man- 
ner to the transitional stage at puberty? (2) Is the advance- 
ment in the two sexes equal at this period of life, and if not, 
how do they differ? We shall take these up in order. 

Evidences of Nodality 

The School Age. — Turning to the first of the problems just 
indicated, it may be worth while, before taking up the dis- 
cussion of actual physical characteristics, to point out that 
this period of the child's life has for centuries been recog- 
nized in a practical way as transitional, in that it represented 
the time for the beginning of formal education. The actual 
chronological age differed somewhat with different peoples, 
but for the most part formal training, as distinguished from 
home training was begun at the age of six or seven years. 

Of China, Douglass wrote (31, p. 165) : " School life 
commonly begins at the age of six, and the youthful learner 
is at once set to learn by heart easy text-books which give in 
short sentences the leading principles of Chinese polity." 
Monroe states that in the old Greek period the Spartan boy 
was taken after seven years of training under the direct care 
of the mother and put under charge of assistants to the paeda- 
monus, being cared for from that time on in public barracks at 
public expense (56, p. 74). Similarly, Athenian boys began 
attendance at school at about the age of seven years (56, pp. 
82-3). Plato, in his ideal Republic would have the boys taught 
music and gymnastics from the age of seven on (56, p. I3.s)- 
Medieval and modern education have fallen into line. The 
legal age for school entrance in most states, and in most 
countries also, at the present time, falls within the sixth or 
seventh year. Thus in the educational practice of most nations 
it has been found experimentally that at about this time of 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 281 

life the child has reached such a stage of development that he 
can undertake the tasks involved in education of a formal 
nature. 

If, now, we turn attention to the more tangible evidences of 
the stage of development, we are led to several considerations. 
There are the matters of growth, both in height and weight, 
dentition, growth of various parts of the body, including 
skull, brain, larynx, eye, etc. Another group of facts also, 
related both to neurological structure and to psychology may 
be added. These have to do with the neuro-muscular control 
of the child. Finally, a few suggestions may be obtained from 
the field of pathology. 

Height and Weight. — As regards growth in height and 
weight, it is generally agreed that the closing years of the later 
childhood period are years of retarded growth. This con- 
clusion is based upon the results of numerous extended inves- 
tigations. Conclusions regarding the earlier years of the 
period are much less definite, partly because of insufficient 
data, partly because of a difficulty in interpreting the mean- 
ing of the growth curves for these years. 

Burk, who summarized the available statistics up to the 
time of his study, 1898, writes as follows (17, p. 257) : 

" If now we turn to Table A of heights, taking, for example, the 
larger American studies of Bowditch, Peckham and Porter, we see that 
the rate of growth is somewhat rapid in the beginning, the sixth or 
seventh year, and decreases with fluctuations until about ten years in 
girls and twelve years in boys, when the prepubertal acceleration sets 
in. This general decrease is to be noticed in all the larger studies, 
though the year of the beginning of prepubertal increase varies a year 
or so. The same decrease in rate from six years up to the time of the 
prepubertal increase is to be observed similarly in the case of girls. 
Curves constructed from absolute annual increases show, as a rule, in 
this childhood' period one or two pronounced fluctuations, but they do 
not occur with a regularity in all charts sufficient to be of assurance 
that their cause is certainly physiological and not merely statistical. 
Nevertheless, it will be observed that the curves are by no means 
regular. . . ." 

Although pointing out thus clearly the irregularities in the 
curve for these early years, Burk goes on to conclude that, in 
the absence of determinative data, it is perhaps better to re- 
gard the period from about six years on as one of a general 
decrease in growth rate, with one or two minor fluctuations. 
The investigations of Combe, Landsperger and Carstadt, made 
upon a comparatively small number of children, but more 
upon an individual plan, are pointed to as justifying this 
view (17, p. 258). 

Smedley, in the Chicago investigations, noticed something 



282 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

of these irregularities in the early school years. Following 
his reference to the pubescent acceleration of growth, he 
writes (84, p. 32) : " The charts seem to show that a similar 
but less well marked period of activity is present from the 
beginning of school life to the age of nine." 

Englesperger and Ziegler (32, Bd. i) found that of the 
children in the first year of school, those between the ages five 
years and nine months and six years were noticeably smaller, 
on the average, than those from si'x years and one month to 
seven years of age. The averages for these periods were : 

Boys Girls 

5 yr. 9 mo. — 6 yr.= 109.65 cm. 106.25 cm. 

6 yr. I mo. — 7 yr.= 11 1.66 cm. 110.77 cm. 

They found considerable differences in height at this period 
between half year, and even fourth year groups. 

A tabulation comparing the weights of these periods showed 
that a smaller percentage of those under six years had gained 
than of those over six years of age. This was on the com- 
parison of weights eight weeks apart at the beginning of 
school. 

Stratz (86, p. 66), in Germany, on the basis of rather 
limited statistics, agrees with a former author, Bartel, in 
making the first four years a period of bodily " fullness." the 
years from five to seven, inclusive, a period of " stretching," 
or spurt of growth, and the years eight to ten a second period 
of bodily fullness, preceding a second spurt from the age of 
eleven to fifteen. 

So far as available statistical material is concerned, growth 
in weight presents a condition similar to growth in height. 
Without giving the data these tabulations may be character- 
ized briefly, and their indications may be stated. Most tabu- 
lations begin with the school age and continue from that 
time on, thus preventing comparisons with the years that 
precede. Usually, also, the number of data for the earliest 
school years are few in number. Again, statistics for weight 
present an added difficulty in interpretation because of the 
greater variability in this factor. So far as comparisons of 
absolute figures may be relied upon, there is only a continuous 
but variable increase in weight from year to year in the two 
sexes, up to the age of nine or ten, when a retardation occurs. 
Boys appear to be slightly superior, throughout the entire 
course. 

There is slight suggestion of a spurt of growth in the be- 
ginning school years, but there is not sufficient evidence to 
establish the point. What is needed here is a collection of 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 283 

more data, beginning with the lower years and continuing 
through the beginning school years. One cannot see in these 
studies of height and weight a definite proof of a character- 
istic of growth at this period. It is a fact, however, that 
from the larger investigations the results strongly suggest a 
slight acceleration. It is also to be remembered that most of 
the tabulations have paid attention to yearly age groups only. 
Much more accurate would be a comparison of age groups 
for fourth years or perhaps for months. 

The rather indefinite studies of development, as indicated 
by increase in growth in height and weight, may be supple- 
mented by some more definite facts with regard to individual 
organs or parts of the body that give more distinct evidence 
of a nodality at the school age. 

Development of Teeth and Jazvs. — The period with which 
we are here dealing is distinctly a transitional one as regards 
the development of the teeth and jaws. These present a num- 
ber of phenomena, transitional as well as developmental in 
their nature, that group themselves about the years in which 
the change from first to second dentition occurs. Some of 
these are very evident, others less so, but altogether they make 
up such a group of developmental processes, so closely asso- 
ciated with each other, and also to other phases of physical 
and mental development that they deserve to be noted con- 
siderably in detail. 

Aside from this, there are also other well grounded reasons 
for dwelling somewhat at length upon this topic, i. Anatom- 
ically, the teeth and jaws are the most important structures 
in the facial part of the skull. Much of the remaining por- 
tion is of rather secondary nature, its purpose being to fur- 
nish place for attachment of muscles or to give proper bracing 
and support for these parts. 2. On the side of physiological 
functioning the teeth and jaws are extremely important. 
Upon them devolves a great part of the preparation of food 
in the process of digestion, not to mention the part they play 
in articulate speech. 3. Again, from the view point of hygiene, 
it may be said that columns of good, sound teeth, so located 
as to bring their chewing surfaces into proper occlusion, are 
requisites of good health. The absence of these conditions 
may lead to any of a number of allied disturbances, to which 
more detailed reference will be made later. 4. Finally, since 
they occupy so prominent a place anatomically, the form and 
general outline of the face are to a great extent dependent 
upon teeth and jaws. It therefore follows that from the view 
point of esthetics the proper formation and development of 
teeth and jaws may not be left unconsidered. Thus we may 



284 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

say that from any of the four view points, esthetic, hygienic, 
functional or structural, development of teeth and jaws de- 
serves the fullest consideration. We shall attempt to con- 
sider the topic from all four of these view points in the follow- 
ing paragraphs devoted to it. 

While most concerned with the transitional phenomena, 
so much depends upon preceding and following developmental 
processes that a rapid review of the entire period of dentition 
may be of value in setting forth more clearly the character- 
istics of the transitional period. In this review, it is assumed 
that the reader's general knowledge of form, names, and com- 
position of the teeth is sufficient to render detailed descrip- 
tions unnecessary. Since similar knowledge with regard to 
the jaws, on the other hand, seems to be less general, descrip- 
tions of the principal structures with which we shall need to 
deal will be included. For the sake of clearness, the facts 
with regard to development of the teeth will be presented first, 
then those with regard to development of the jaws. With 
these two groups of facts before us, we may next proceed to 
discuss their relationship and its significance, and arrive at 
some conclusions. With these hints as to method of proced- 
ure before us, we turn next to the presentation of the facts. 

Although the eruption of the first or temporary teeth from 
the gums does not take place until some time after birth, the 
formation of their crowns begins very early in the developing 
embryonic jaw. Their calcification is already far advanced 
at the time of birth. The early formation and development 
of these is somewhat as follows : Above the gums, along the 
rudimentary jaw of the embryo, there is formed very early 
a ridge of epithelial cells. At each of the ten points at which 
a tooth crown is to be formed, a depression or invagination 
occurs in this ridge, pushing on downward into the jaw in 
a line, as it were, or tube, and expanding at the end into a 
bell-shaped structure, — the enamel organ. Gradually the 
enamel organ grows down over the top and sides of a small 
mound-like enlargement that rises up from the deeper tissue, 
— the dental germ. Again a little later the connection of the 
enamel organ with the epithelial ridge above is lost, enamel 
organ and dental germ together become isolated from the 
surrounding parts and enclosed in a " dental sac," and within 
this sac the two organs proceed to build up the parts of the 
tooth crown. Out of the soft cells that make up the enamel 
organ is formed the enamel ; out of those of the tooth germ 
is formed the dentine or ivory of which the inner part of the 
tooth is composed, and within which, again, is the open cavity 
containing the pulp. 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 285 

The transformation of these soft cells into the hard struc- 
tures of the crown is accomplished by means of the deposition 
of lime salts within the cells themselves, and is usually spoken 
of as a process of calcination or calcification. The processes 
are not the same in both cases, however. While the cells of 
the enamel organ become changed into solid crystals, those 
of the dental germ receive the lime deposits only around the 
outside in such a way that the resulting structures are elongate 
tubes. The central, uncalcified portions remain as fine fibrils 
which are connected with the soft pulp of blood-vessels and 
nerves that fill the inner cavity of the tooth. The dentine 
tubes thus formed are of considerable length and extend out- 
ward radially from the pulp cavity to the enamel " roof " of 
the tooth. 

The direction in which the calcification proceeds differs in 
the two organs. It will be remembered that the enamel organ 
folds over and encloses the dental germ. Now, the calcifica- 
tion begins at the contiguous surfaces of the two organs and 
proceeds in both directions. For the enamel cells, then, cal- 
cification proceeds from the inner surface toward the outer; 
for the dentine cells, it proceeds from the outer surface in- 
ward toward the pulp cavity. 

Enamel and dentine differ also in another way. The enamel 
crystals receive no more nourishment after being once formed. 
The dentine cells, on the other hand, continue to receive some 
nourishment throughout the life of the tooth by means of 
the soft fibrils in the central tubular portions. (St,, p. 31.) 

As the development of a crown proceeds beneath the gums 
there is deposited around it a layer of bony substance, so 
that by the time it is completed it is almost enclosed in a 
bony case or crypt. The top of the crypt is open, though 
the aperture is not large enough for the crown to pass 
through without absorption of some of the tissue from its 
edges. This is what occurs at the time of eruption of the 
crown. 

After the manner thus described there are formed ten tooth 
crowns in each of the jaws. Their calcification is not entirely 
completed by the time of birth, but it is completed within 
the first few months of life. Then they emerge from the 
gums to form the " temporary set " that functions during the 
early years of the child's life. Of these, the incisors and 
canines are small, as compared with the corresponding teeth 
that follow. The bicuspids, or milk molars, on the other hand, 
are larger than the permanent bicuspids that follow. In this 
way ample provision is made for the mastication of such 



286 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

foods as the child is able to digest and assimilate during his 
early years. 

Some weeks after birth the crowns of the temporary set 
are completed and begin to erupt from the gums. The first 
become visible at about the sixth to eighth month of life, 
usually, and at the age of about two and one-half to three 
years the child is equipped with a full set of twenty. Ap- 
pearance is usually in groups, beginning with the central in- 
cisors and proceeding, in a general way, backward from these, 
with intervals of time elapsing between the several groups. 
Witzel reports the usual time for the eruption of these, as 
given by Thomas and Baume, to be as follows (98, p. — ) : 

Central incisors 6-8 mo. 

Lateral incisors 6-12 mo. 

Anterior bicuspids 12-16 mo. 

Canines 15-20 mo. 

Posterior bicuspids 20-30 mo. 

The basis for this statement is not given, no mention being 
made of actual investigation. The periods given are those 
within which the eruption from the gums usually occurs. It 
is possible for the teeth to appear much later, however, and 
yet be normal. It is also possible for a few of the crowns 
to be already visible at birth and the teeth be normal, though 
this is very often the result of diseased conditions. 

The process by which a tooth crown erupts is somewhat 
complex. The edges of the opening in the bony ciypt must 
first be reabsorbed, making room for the crown to push 
through. The gums that form the covering are next absorbed. 
While this is going on and the crown gradually pushing up- 
ward, additions are made to the root from cells at the base 
of the crown, and, once the final position is attained, the 
root becomes fastened into place by the bony tissue built up 
around it. The root canal remains as a rather wide opening 
for some time, however, the dentine being built up gradually 
until the root is solid, except for the narrow canal through 
which the vessels and nerves are admitted to the pulp cavity. 

The tissue built up around the teeth and within which their 
sockets are found is known as the alveolar border of the 
jaw or alveolar process. It is developed with the teeth and 
apparently for the specific purpose of holding them in posi- 
tion. Fuller description of it may be reserved until later. 
A description of the means by which the tooth roots are 
firmly fastened within it, however, is in place at this point. 
This can best be given in the words of Dr. Angle, taken 
from his paragraph on "Peridental Membrane" (i, p. 122). 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 287 

" The peridental membrane is a strong, fibrous membrane forming a 
close, cushion-like investment of the roots of the teeth, and is the 
medium of attachment between the alveolar process and the cementum. 
It is composed largely of inelastic connective tissue, and is richly 
supplied with nutrient vessels, nerves, cells, and glands. Its function 
is three-fold : 

" First, vital, for the formation of the alveolar process on one side 
and the cementum on the other. 

" Second, sensory, through which the most delicate touch of the 
tooth is felt. 

" Third, physical, holding the tooth in position in the alveolar socket, 
and resisting the movements of the teeth in the various directions. It 
also supports the soft tissues about the teeth." 

Continuing, Dr. Angle enumerates the kinds of cells of 
which the peridental membrane is composed as, /, fibroblasts, 
for the formation of fibers of the membrane ; 2, osteoblasts, 
for the formation of the alveolar process ; 5, cementoblasts, 
for forming the cementum ; 4, osteoclasts, for disintegrating 
calcified tissue; and finally, 5, glands, the function of which 
is as yet imperfectly understood (i, p. 123). 

Malposition of temporary teeth is rare. When it does occur, 
it is easily corrected, under normal conditions, by means of 
the pressure from lips and tongue. But while this is true, 
abnormal conditions may as readily cause the teeth to be 
moved from their proper positions and thus bring about a 
malocclusion. 

But the temporary crowns are not formed alone in the 
embryonic jaw. The beginnings of the permanent crowns are 
also present at a very early stage. Very early in the develop- 
ment of the enamel organ of each of the temporary teeth a 
second line or tube of epithelial cells pushes down by its 
lingual side. It appears as a branch of the tube which de- 
velops into the enamel organ of the temporary tooth. In 
structure, too, it is similar, and its development, later, after 
the manner described for the temporary tooth, results in 
the formation of the crown of the permanent tooth. 

Aside from the ten corresponding to the crowns of the 
temporary set, there are also six other germs in each jaw, 
as the beginnings of the molars of the second set. The child 
at birth, then, has in each jaw the almost completed crowns 
of the ten teinporary teeth and also the germs of the sixteen 
permanent teeth at various stages of development. The com- 
pletion of the permanent crowns is of course later than that 
of the temporary, their time of most rapid growth, according 
to Pedley (62) being from birth to three or four years of 
age. Johnson places the critical period for their calcification 
at from birth to the age of five years, that of the first perma- 
nent molars having been begun even before the birth of the 
child (51). 



288 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

The time of these processes is given more in detail by 
Witzel (98, p. 17) : 

" The calcification of the crowns of the incisive teeth begins between 
the first and second year and the calcification of the canine tooth in 
the third year. In the fifth year of age the tuberosities for the second 
molar tooth are developed and in the ninth those for the third. About 
the time of the ninth year no remarkable processes of calcification take 
place in the crowns, except in the wisdom tooth, but the roots are not 
everywhere fully developed. . . ." 

The ages mentioned are of course only approximate, and 
vary within wide limits. 

From this it follows that from birth to about five years of 
age is a critical period for all the permanent set, except the 
wisdom teeth. During this period the dental germs, many 
of which have begun development at the time of birth, attain 
their final form, make their most rapid growth and undergo 
a great part of the process of calcification. In this connection 
it should be emphasized that when once formed and com- 
pletely calcified, these crowns are adult crowns, as large as 
they will ever be, and subject to neither growth nor repair, 
so far as the organism to which they belong is concerned. 
Completion of the crowns is accompanied by enlargement of 
the alveolar border and growth in some parts of the jaw, 
with considerable redistribution of the inner structures. 

Thus far we have noted the principal features in the forma- 
tion and calcification of the temporary crowns, marked the 
important changes involved in their eruption and in their 
fixation into position by means of developing root structures 
and alveoli, and have traced the important steps in the process 
by which the permanent crowns are formed, developed and 
calcified within the alveolar portions of the jaws. Each one 
of these is a developmental feature characteristic of the earlier 
years, and constitutes a step in the preparation for the coming 
of the permanent teeth. The time immediately preceding sec- 
ond dentition is therefore a remarkable one for the child, 
considered from the view point of his dentition. Within his 
jaws there are i, a full set of twenty functioning temporary 
teeth, 2, the practically completed crowns of their twenty suc- 
cessors, many of which are larger, j, the completed crowns 
of the four first permanent molars and practically completed 
crowns of the four second molars, and 4, the only partially 
developed germs of four wisdom teeth or third molars. This 
is the normal condition of the child's jaws at the age of five 
or six years. Transition to the second dentition usually begins 
very soon afterward. 

In discussing the eruption of the permanent crowns we may 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 



289 



first give attention to the time of their appearance, and then 
turn to the description of the process by which it is brought 
about. 

Time of appearance of the permanent teeth has been made 
the object of a number of investigations. Some of these are 
of no vakie for our purpose, since they do not differentiate 
the sexes. Of the three available that do, one is not extended, 
but the other two are sufficiently so to make their results 
valuable. 

First let us turn to the statistics of Boas and Wissler. Their 
material was a series of plaster casts taken from the palates 
of 219 boys and 276 girls. They therefore contain data for 
the upper jaw only. The following Table A is their table 
numbered " XI C." giving results in percentages (ii, p. 34) : 

TABLE A. 

Percentage of Children Having Permanent Teeth. 



Age 


Boys 


Girls 


In. 
Inc. 


Out. 
Inc. 


Can. 


Bic. 


ist 
Mol. 


2nd 
Mol. 


In. 
Inc. 


Out. 
Inc. 


Can. 


Bic. 


ist 
Mol. 


2nd 
Mol. 


6 


30 


4 






65 




38 


9 


6 


15 


83 


2 










7 


40 


6 


3 


3 


83 




79 


28 


2 


41 


92 




8 


81 


26 




19 


100 




84 


48 


9 


45 


93 


6 


9 


97 


67 




30 




7 


100 


59 


9 


45 


100 


2 


10 


100 


63 


33 


66 




3 


94 


82 


14 


73 




8 


1 1 




95 


61 


100 




9 


96 


96 


73 


83 




20 


12 




100 


85 






38 


100 


100 


86 


100 




32 


13 






91 






68 




88 


88 






68 


14 






IOC 






66 




90 


9c 






90 


15 












75 




100 


IOC 






100 



Averages and variabilities were computed for the time of 
appearance of the several teeth and found to be as follows 

(12, p. 35): 

Boys 

Inner incisors 7 • 5 ± i • 5 y- 

Outer incisors 9.5^2.1 

Bicuspids 9.8±i.6 

Canines ii.2±i.4 

Second molars 13.2 ±2.0 



Girls 

7.0 ±1.6 yr. 

8.9± 2.1 

9.0 ± 2.8 
1 1 . 3 ± I . o 
12. 8± 1.6 



290 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 






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PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 



291 



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292 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 



The investigation of Berten was much more extended. He 
collected data from some 3.345 children in Germany, of ages 
ranging from five and one-half to thirteen and one-half years. 
In the accompanying Table B are presented the numbers of 
teeth present for each half-year group within these ages. 
This table condenses the data found in Berten's tabulation 
(8, pp. 278-9). Boldface figures indicate groups where 100 
per cent, were found present. 

A report of an investigation much more extaided than 
either of these appeared in recent years. Dr. Rose has tabu- 
lated the number of teeth found present in the several groups 
in case of 41,021 children in Germany, Sweden, Denmark, 
Holland, Belgium, Bohemia and Switzerland. His tabulation 
differentiates upper and lower teeth, also sex groups, and 
gives the averages and variabilities for the several tooth 
groups. 

Table C is his " Table XIV," in which the results of the 
investigation are summarized {^J, p. 564) : 



TABLE C. 

Eruption Time of Permanent Teeth in 41,021 School Children 

FROM Germany, Sweden, Denmark, Holland, Belgium, 

Bohemia and Switzerland. 





Boys^2 1,139 


Girls=i9,882 




Average 

eruption 

time 


Eruption 

time 

varies 

between 

ages 


Average 

eruption 

time 


Eruption 

time 

varies 

between 

ages 




Yr. Mo. 


Yr. Mo. 


upper jaw 
Incisor I... 
Incisor II .. . 

Canine 

Premolar I . 
Premolar II. 

Molar I 

Molar II.... 


7 8 

8 II 
12 2 

10 5 

11 4 
6 7 

12 9 


5 
6 

7 
6 
6 
5 
9 


5-1 1.5 Yr. 
-(?) " 

5-15- 
5-14. 
5-15- 

- 9-5 " 

-15- 


7 5 ( -3 Mo.) 

8 6 ( -5 " ) 

II 7 ( -7 " ) 

10 I ( -4 " ) 

11 I ( -3 " ) 
6 6 ( -I " ) 

12 5 ( -4 " ) 


5 
6 

7 
6 

7 
5 
9 


5-1 1. Yr. 

-(?) " 

-15- " 
5-14.5 " 

-15- 

-10. " 

-IS- 


LOWER JAW 

Incisor I . . . 
Incisor II .. . 

Canine 

Premolar I. 
Premolar II. 

Molar I 

Molar II.... 


6 10 

7 II 
II 2 

11 3 

12 

6 5 
12 3 


5 
6 

7 
7 
7 
5 
9 


—ID. Yr. 
-12. " 
-15- 

-14-5 " 
-15- 
-10. " 

-15- 


67 ( -3 Mo.) 
7 7 ( -4 " ) 

ID 3 (-11 " ) 

10 8 ( -7 " ) 

10 7 ( -5 " ) 
6 3 ( -2 " ) 

11 9 ( -6 " ) 


5 
6 

7 
7 
7 
5 
8 


-II. Yr. 
-12. 

-14. " 
-14.5 " 
-15- 
- 9- 
-15- 


Avg. of the 
total 14 
eruptions. 


9 lO.O 




9 5.4 ( -4.6 Mo.) 





PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 293 

Careful study of these tabulations will show that they are 
in agreement as to the essential points regarding the time and 
the order of eruption of the permanent crowns. Each one 
confirms the prevalent view that transition to second denti- 
tion begins with the eruption of the first permanent molars. 
This is evident in the tabulation of Berten, and in the averages 
from the very extended investigation of Rose. Berten writes 
that in only three cases did he find the transition to the perma- 
nent teeth beginning before the appearance of any molars 
(8, p. 271). 

Incidentally it should be noted that the time for the appear- 
ance of the first molars is in the seventh year. Berten's table 
indicates that practically all appear between the age of six 
years and seven and one-half, while Rose's averages all fall 
between the ages six years and three months and six years 
and seven months. 

Again, the more extended investigations of Berten and 
Rose have furnished abundant evidence in confirmation of the 
view that the lower teeth appear, on the average, earlier than 
the upper, except, perhaps, in case of the canines and bicus- 
pids. In all the investigations a considerable variation in the 
time of appearance for the several tooth groups is evident. 
From this it follows that dentition does not run a parallel 
course in all children. Variation in time of appearance is 
least in case of the first molars and grows progressively 
greater with each succeeding tooth group, up to the bicuspids 
and canines. 

The order in which the permanent crowns appear is repre- 
sented in these data. According to them it runs : first molars, 
inner incisors, outer incisors, first bicuspids, after which the 
order of the remaining groups is somewhat confused. Berten 
states (8, p. 274) that most often we find these groups ap- 
pearing in such a way that the lower canine follows the first 
bicuspids, and is followed, in turn, by the upper second bi- 
cuspid ; then the lower second bicuspid appears, and the upper 
canine brings up the rear. 

Finally, before leaving this topic, the point of sex difiference 
in time of eruption of the teeth should be pointed out. In 
each of the three tabulations it is clearly evident, beginning 
with the first molars, at the very beginning-time of second 
dentition. Rose's results show the girls to be two months 
earlier in eruption of lower first molars ; one month ahead in 
eruption of upper first molars, on the average. The actual 
difference of time is not so evident in Berten's table because 
of the form in which it is presented, but comparison of the 
numbers of the teeth present show that the results would be 



294 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

in agreement. Presented in the form of curves showing the 
percentages of teeth present in the various groups, Berten's 
data show very clearly that this is true. 

The processes by which the eruption of the permanent 
teeth is accomplished deserve some further consideration. 
Evidently the temporary structures must first be disposed of. 
This is the first step in the eruption of the permanent set. 
It is accomplished by a sort of reverse process to that by 
which the temporary roots are builded down and fixed within 
the alveolar border. Beginning at the lower parts, the roots 
are again reabsorbed, along with the bony case of their 
sockets, even before the term of functioning of the teeth is 
completed. Radiographs showing partially reabsorbed roots 
present very much the same appearance as those showing par- 
tially developed ones. Apparently the reabsorption, or resorp- 
tion, as it is often called, is incited by the pressure of the 
developing permanent crowns below. At any rate, in normal 
cases the process is sufficiently advanced by the time the per- 
manent crowns are ready to appear to allow the temporary 
tooth to be readily removed with very slight disturbance and 
very little pain. 

Evidently here are processes in which the different types 
of cells in the peridental membrane described above, especially 
the osteoclasts, play a very important part. Pedley and Har- 
rison (63, p. 52) would credit the leucocytes with an impor- 
tant part in the resorption process also. 

Aside from the resorption of the temporary roots there 
is also a process of resorption of the cancellated tissue that 
surrounds the deeply embedded crowns, allowing for their 
passage upward toward the surface. In case of the molars, 
this includes the absorption of part of the cortical bone along 
the borders of the jaws where there have been no preceding 
temporary teeth. 

The growth process by which the crowns emerge, making 
additions to the roots while so doing, is not essentially dififer- 
ent from that of the temporary ones already described. Build- 
ing up of the roots seems to be a somewhat slower process 
in this case, and their final cementing into place more per- 
manent. This latter is rather an osseous change and will be 
mentioned more in detail later, but it should be noted in this 
connection that the order is always first tooth position, then 
adjustment of foundation. This is true regardless of whether 
the position assumed is normal or abnormal. The bony foun- 
dation builds to the tooth, whatever may be the position it 
assumes. 

Again, difference in size, especially of incisors and canines, 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 295 

is greater in the upper than in the lower jaw, so that read- 
justment of the two columns of teeth to each other becomes 
necessary. This is a fact of considerable importance for the 
normal occlusion of the teeth of the permanent set. Whereas 
the upper and lower teeth of corresponding names fit end to 
end in the temporary set, in the permanent, the greater size 
of the teeth in the upper column cause a backward shift along 
the sides. The normal condition is therefore for each molar 
and bicuspid to articulate, not with a single antagonist in the 
other jaw. but with two teeth. 

So much for the phenomena of dentition. The treatment 
is inadequate, but possibly sufficient facts have been presented 
in this brief review to indicate that the beginning of later 
childhood is without a doubt a transitional period as regards 
the teeth. Preceding this period time and material are both 
devoted to the task of providing temporary structures and 
preparing permanent crowns ; with the eruption of the first 
molars at this period, however, is ushered in a series of re- 
markable changes, every one of which is a step in the direc- 
tion of dental maturity. Dr. Port (65) stated the case nicely 
when he referred to this period of life as one at which, for the 
dentist, the child becomes adult. The significance of these 
phenomena becomes greater when they are associated with 
others closely allied to them, and, in a way, depending upon 
them. To some of these we shall next give attention. 

Paralleling that of the teeth, there must occur a pro- 
gressive developmeiit of the bony arches of the jaws that 
form their foundations. Structurally, both jaws are complex, 
and are in very close relationship to the other parts that' 
make up the facial portion of the skull. Thus the upper jaw 
forms the principal bone of the face, taking part in the 
formation of the hard palate, the floor of the orbit and the 
floor and lateral wall of the nasal cavity (71a, p. 50). Cryer 
states (27, p. 31) that in a surgical operation removing 
a right or left maxilla, " the inferior turbinate, portions of 
the lachrymal, the palatal, the malar, and the ethmoid bones 
will probably be removed with it." The lower jaw, on the 
other hand, has the distinction of being the strongest and 
thickest bone of the face. It is made up of the arched por- 
tion known as the body, and the two ascending portions called 
the rami, each of which has a flat, pointed projection at its 
anterior edge for the attachment of muscles, and at the 
posterior edge a convex process which hinges with the for- 
ward portion of the temporal bone and allows for the move- 
ments of the jaw. 

Leaving aside for the moment the details of structure, we 



296 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

may generalize with regard to the arched portions of the 
two jaws by saying that in either case, the essential features 
are (i) a basal osseous arch composed of an outer shell 
of cortical bone filled in with spongy, cancellated tissue, and 
(2) an alveolar border consisting of two thin, hard, compact 
plates, an inner and an outer, fitting close to the roots of the 
teeth, between which is the looser cancellated portion sur- 
rounding the roots of the teeth, and within which the more 
compact, shell-like cases surrounding the roots are contained. 
The whole arrangement of the jaws, both with reference to 
each other and to the remaining portions of the face and 
skull, is such as to withstand the strain of muscular con- 
tractions in chewing, and at the same time protect against 
forces from without, such as blows, by diffusing them in 
a way to prevent their being transmitted to the brain case 

As already intimated in a previous paragraph, the develop- 
ment of the jaws begins very early in the embryo. Accord- 
ing to Ouain's Anatomy (71), the order for the begin- 
ning of calcification of the bones is : first, the clavicle ; second, 
the inferior maxillary (mandible) ; and third, the superior 
maxillary (maxillae). The Text-Book of Cunningham places 
the beginning at about sixth or seventh week of foetal life 
(28, pp. 144-5). Witzel would seem to agree as to time, 
since he published a plate (98, plate 3), showing calcification 
of the mandible in a foetus of six weeks. 

In case of either jaw, calcification begins in a number of 
centers which later unite. The final completion of this 
process does not occur in the mandible until some time after 
birth (usually during the course of the first year), when the 
two halves unite. 

Extended and accurate investigations of the growth of the 
jaws from this time until the beginning of second dentition 
are very few. On a few points, however, authorities seem 
to be in agreement, so that we may characterize in a general 
way the principal developmental features of this period. 
Naturally we turn first to longitudinal growth. After the 
completion of the first year, or at least after the completion 
of first dentition, there is little or no growth in those 
portions of the arches containing the temporary teeth. If 
any occurs at all it is very small in amount. With the 
appearance of the teeth there is a lengthening of the ascend- 
ing portions of the lower jaw, thus making room for the 
teeth and their alveolar borders. The relationship of this 
development to the order of the appearance of the teeth con- 
stitutes one of the nice adjustments of nature, as Pedley and 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 297 

Harrison (63, p. 42) have pointed out. In general, the order 
of tooth appearance is from front to back. By this means 
time is gained for the growth in the length of these branches, 
while at the same time there is not left an " open bite " in 
the middle of the arch. 

As regards internal structure, arrangement of the fine bony- 
particles or trabeculae remains for the most part regular, 
though there are some changes having to do with strengthen- 
ing the jaws and adjustment to the developing crowns of 
the permanent teeth (98). 

The rapid growth of the jaws at the time of second den- 
tition is a well known fact. It is evident in the changed pro- 
portions of both jaws and face, with the resulting change in 
facial expression, and is also inferred from the fact that the 
second set contains a greater number and, to all appearances, 
larger teeth. 

Growth is largely dependent upon the development of the 
teeth, and is therefore not uniform in all parts of the jaws. 
A number of investigators have attempted to answer the 
question as to whether there is any longitudinal growth in 
those portions of the arches bearing the temporary or decidu- 
ous teeth at the time of second dentition. Zsigmondi (106) 
reports the results from a long series of these investigations, 
and in addition describes an investigation of his own, in 
which, by the use of plaster casts, he employed a new method, 
obtaining records of the same jaws at different stages of their 
development. 

Difficulties of method are everywhere apparent, not the 
least of which is that the measurements give a record, not of 
the differences in the basic part of the jaw, but rather of those 
in the dental arch or the alveolar border only. Re- 
ferring in part to the results reported by Zsigmondi, in part 
to the original articles themselves, and comparing carefully, 
it seems only safe to say that there is not conclusive evidence 
that any longitudinal growth occurs in that portion of the 
alveolar arch lying between the first permanent molars during 
the period of second dentition. Since this is true, there is 
likewise no evidence to show that longitudinal growth occurs 
in the basic portions. 

That the dental arch in the upper jaw becomes larger is 
not disputed, but attention is called to the fact that here the 
teeth with their alveolar border slant outward, while in the 
lower jaw they slant rather inward, so that the question of 
longitudinal growth of the basic part of the jaw is still left 
unanswered. Besides, the question as to the presence or 
absence of growth is most often raised with reference to the 



298 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

lower jaw, the result being that most investigations have had 
to do with it, and have secured data pointing more or less to 
conflicting conclusions. However, while conclusive proof is 
lacking, there is not general agreement that growth does not 
occur. More recently Cryer (27, p. 14), who bases his con- 
clusion upon the study of the anatomical arrangement of the 
inner structure of the mandible, has declared in favor of 
growth. Angle also seems to hold this view (i, p. 91). 

While growth in the " deciduous arch " is still questioned, 
on one other point authorities are agreed. While the perma- 
nent incisors and canines require a greater amount of space 
than their predecessors, the greater requirement is partially 
compensated for by a lesser space requirement on the part of 
the permanent bicuspids, which are smaller. The actual need 
for growth in these portions of the jaws is therefore much 
less than it would be were the permanent teeth uniformly 
larger than their predecessors. The compensation is much 
less nearly complete in the upper than in the lower jaw, thus 
giving a second partial explanation of the fact that the upper 
permanent dental arch is apparently larger, while the increase 
in the size of the lower is questioned. 

Let us turn attention next to the posterior portions of the 
jaws. It should be noted first that authorities generally agree 
that growth of these portions is dependent upon the develop- 
ment and eruption of the molar crowns. In either jaw the 
growth must be sufficient to make room for the three molar 
teeth on each side. The development of these crowns seems 
to be the signal for growth of this portion of the jaws. This 
is especially noticeable in the lower jaw. " The cutting of the 
first molar tooth and the formation of the crown of the second 
cause in the following years of life a strong longitudinal growth 
of the maxillary body, . . ." writes Witzel (98, p. 59). 

As in case of the anterior portions of the arches, there is 
much disagreement as to the exact process by which the 
increase is brought about. Some authorities, such as Cryer, 
hold that growth is general along the jaw and that each erupt- 
ing crown pushes the ones anterior to it forward {2'j, p. 14). 
Others take the position that the growth is only at the ex- 
treme posterior portion, and that much of it is due to absorp- 
tion and deposition of the bone substance. Humphry quotes 
Tomes (48, p. 3, footnote) to the effect that these processes 
are shown by the examination of the histological structures 
at time of growth. Humphry also tested the growth. in the 
lower jaws of young pigs by piercing the ascending portions 
and tying wires about the anterior and posterior borders. 
Later, when the pigs were killed, the wires at the anterior 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 299 

border were found to have either become loosened or dropped 
out, showing that resorption of bone had taken place, while 
the wires at the posterior borders were found in deeply in- 
dented notches formed from the progressive deposition of 
bone above and below them (48, p. 3 ff.). 

Besides the horizontal growth in the arches of the jaws, 
adjustment to the greater space required between them to 
accommodate the larger permanent set is accomplished by 
means of a growth in the length of the ascending portions, 
or rami, of the mandible. With the longitudinal growth down- 
ward and backward the angle of the jaw becomes more acute, 
approaching a right angle, though this is apparently due in 
part also to the development of the teeth and alveolar border. 
Finally there may be mentioned a group of changes of inner 
structure. Rearrangement of the teeth brings about a neces- 
sary redistribution of their neural and vascular supply. In- 
crease of masticatory surface, accompanied by a growth in 
strength of the muscles used in mastication, causes a strength- 
ening of the basic portions of the jaws ; lastly, as a result of 
rearrangement of the lines along which the forces are exerted 
in mastication, as well as of growth, there occurs a new 
arrangement of the bony trabeculae within the jaws to adapt 
to the new conditions. 

In addition to that of the jaws, some other developmental 
factors appear to be very closely related to dentition. Pos- 
sibly most prominent among these is the growth of the face, 
due in part, of course, to the increasing size of the jaws. 
West found in his Worcester investigation (97) that there 
are pretty distinct periods in the development of the female 
face, the first division point being at about the seventh year. 
Transitions from one type to the one next following seemed 
to be rather abrupt. Rose found from head and face meas- 
urements of more than 45,000 children of different nation- 
alities that the face lengthens much more rapidly during the 
time of change of teeth than it does in later years (75, p. 
711). Facial index increased in length some three and one- 
half degrees between ages seven and thirteen (75, Table 5, 
p. 706). 

Greater masticatory ability seems to be accompanied by 
an inner psychic change. Bell (7) found in his study of the 
psychology of foods that taste becomes " mentalized " at 
about the age of seven as it has never been before. He speaks 
of this as a stage of " teasing to taste." He found also a 
tendency to make every possible mixture at this period, and 
an increased interest in medicine, with a tendency to taste it. 
Dr. Wright (100) finds that periods of enlargement of the 



300 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

tonsils without inflammation coincide with the times when the 
groups of molars are erupting. He finds that after giving 
the tonsil prophylactic treatment, when necessary, and wait- 
ing for the tooth to erupt, the return of the enlarged tonsil 
to the normal will follow in a high percentage of cases. Dis- 
appearance of abnormal tonsilar conditions also follows the 
treatment of carious teeth in many cases. 

He contends that tonsilar enlargement without infection is 
but an expression of the normal functioning of lymphoid 
tissues in that region, especially active at times of tooth erup- 
tion because of additional requirements in the way of caring 
for waste material which results from rapid bone resorption, 
etc. The second period when this condition is liable to be 
present coincides with that for the eruption of the first per- 
manent molars, and therefore in a general way also with 
the period of life in which we are here especially interested. 

One hesitates to leave this topic without dwelling for em- 
phasis upon the importance of dentition for development at 
the beginning school age. Referring to the relationship of 
the teeth to nutrition, Crampton (26, p. 354) has spoken of 
tooth appearance as " the indication of successful growth and 
the earnest of further preparation for growth." 

Again, importance of dentition stands out clearly when one 
takes into account the number of conditions by which its 
progress is affected. The great variation in time of appear- 
ance has been noted. There are many explanations for this. 
Early or late dentition have often been charged up to here- 
dity, and facts regarding the first set, such as those presented 
by Holt (45, p. 28) and Rosenhaupt (79) would seem to 
indicate that there is reason for doing so. Rose has found 
that permanent teeth appear earlier among Swedish than 
among German children, thus showing the influence of race 
{77). He would also credit the chewing of coarser foods 
with some influence in this case. Again, in the same investi- 
gation. Rose found dentition earlier in children of the higher 
schools than in those of the Volkschule, and earlier in chil- 
dren of city than those of rural communities. This is ex- 
plained as due to differences of nourishment, and to some 
extent to better racial selection also. The importance ot 
nourishment while the crowns are developing, therefore dur- 
ing the first five or six years of life, is emphasized by many 
authorities. Bell (7), without giving his authority, states 
that it is reported southern children erupt their teeth earlier 
than northern. Finally, it is recognized that diseases influ- 
ence dentition. Holt (45, p. 28) says syphilitic children are 
prone to early dentition, in which case rapid decay is likely 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 3OI 

to follow. Rickets is usually credited with having a retarding 
influence. Rose tested this {jy, p. 569) by comparison 
of children with normal teeth and those with hypoplasia, or 
deficiency of enamel. Among 10,020 children, he found a 
slightly later eruption time in the latter group. Latest denti- 
tion is seen in cretinism (45, p. 29). 

The complexity of the problem is evident. Berten says 
(8, p. 267) that whoever has given only slight attention to the 
eruption of the teeth will have found that the time varies 
with race, climate, sex, constitution and disease, and in part 
to sports of nature. 

Composition of the tooth crowns is apparently affected by 
many of the same influences, especially conditions of nourish- 
ment and disease. Lack of lime in food and water may cause 
poor dental structures, with deficient enamel, and therefore 
poor protection. Dr. Burnham (18, pp. 296-7) reports a 
number of investigations indicating that regions poor in lime 
show a high percentage of carious teeth. Pedley and Harri- 
son (63, p. 47) emphasize the use of the teeth as beneficial, 
in that it increases blood supply and thus brings more nour- 
ishment. The disease of rickets apparently deprives the teeth 
of sufficient lime salts, being accompanied usually by hypo- 
plasia, a condition in which the enamel is deficient. 

Finally, we may cite the response of the organism to dental 
conditions, as evidence of the importance of the latter at 
the school age. Among others, Jessen (50, p. i) quotes these 
conclusions from Rose's " Zahnvcrdcrbniss und Zcnsur " 
(Deuts. Monats. f. Zahnheilk., 1904) : 

" I. The physical development of school children is greatly 
influenced by defective teeth. 2. The poorer the physical 
development, the poorer also is the mental power (" Spann- 
kraft ") of the children. 5. The poorer the teeth, the worse 
are, on the average, the grades of the children." In his arti- 
cle on the " Hygiene of the Teeth " Dr. Burnham writes 
(18, p, 298) : " Of the various disorders frequently caused or 
aggravated by decaying teeth are not only enlarged glands 
of the neck, headache, neuralgia, earache, but indigestion, 
heart trouble, irritation of the nervous system, epilepsy, and 
perhaps chorea and other neuroses." 

Preservation of a full set of sound temporary teeth and 
regulation of their positions when necessary are requisites for 
proper development of both teeth and jaws at time of second 
dentition. Premature extraction, too long retention, caries or 
malocclusion in case of the temporary set may be the cause 
of improper development of the jaws with impaction or with 
abnormalities in position of the permanent crowns. 



302 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

Some experiments upon animals would seem to indicate 
the dependence of proper development in jaws and face upon 
a full set of functioning teeth. Walkhoff (92) cut one tem- 
poral muscle of a dog four weeks old, compelling him to 
chew only on the other side. Within three months a differ- 
ence between the development of the two sides of the jaws 
could be detected, and at the end of a year the functioning 
side was much larger and stronger than the other. Dr. Baker 
(5) performed a similar experiment by grinding the teeth of 
young rabbits, preventing occlusion in one-half of the jaw. 
Not only the jaws, but the parts of the skull to which the 
muscles of mastication were attached showed the effects by 
their greater size and strength on the functioning side. The 
unused sides remained undeveloped. The prepared skulls 
showed a distinct asymmetry. 

While emphasizing the point that the presence of all the 
teeth is essential, Dr. Angle has stated (i, p. 17) that, "in 
function and influence some are of greater importance than 
others, the most important of all being the first permanent 
molars." He explains further that this is true because, /. 
they are largest and firmest in their attachment, 2. they have 
the most important location in the arches, j. their length de- 
termines the separation of jaws and length of bite, thus 
contributing to facial proportions, 4. they are first in position 
and influence other tooth positions, and 5. they are most 
constant in time of eruption and in the assumption of normal 
positions. 

From all these facts, and especially in view of the close 
relationship of tooth development and nutrition, it must fol- 
low that dentition is a matter of prime importance in the 
early years. It would perhaps not be too much to say that, 
from among all the factors which may and should be con- 
sidered for such a purpose, dentition is the best single indi- 
cator of the stage of physical development which a child 
has reached at any time during these early years, or, as some 
would state it, of physiological age. 

Having dwelt somewhat at length upon this very import- 
ant phase of development, we may bring together the prin- 
cipal points in this brief summary: 

I. The development of the teeth and the parts closely re- 
lated to them, particularly the jaws, give evidences of a 
transitional stage at about the time of the beginning school 
years. The loss of the temporary and the eruption of the 
second, permanent, more numerous, adult-sized set of teeth 
is begun at this time, producing a new, different method of 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 303 

articulation. This is accompanied by rapid growth in certain 
portions of the jaws, with considerable rearrangement of the 
inner structures, resorption and deposition of bone sub- 
stance, etc. 

2. Normally, the transition is begun by the eruption of 
the first permanent molars, at about the seventh year, after 
which temporary tooth groups are replaced by the perma- 
ment in the order ; inner incisors, outer incisors, first bicus- 
pids, with canines and second bicuspids following in variable 
order, and followed in turn by second molars. Wisdom teeth 
come much later. 

J. The time of tooth appearance in dififerent children 
shows considerable variability, beginning with the early years, 
clearly evident at the time the first molars erupt, and increas- 
ing rapidly with the progress of dentition thereafter. 

4. Sex differences are apparent in the eruption time of the 
permanent teeth, those of the girls appearing earlier, on the 
average, than those of boys. Here also, the difference in- 
creases with the progress of dentition. 

5. The vital significance of dentition as a factor in develop- 
ment is shown by its close relationship to nutrition, by its 
close relationship to the growth of other parts, such as jaws, 
face and skull; by the many influences, such as nutrition, 
race, sex, etc., by which it is influenced ; and by the reaction 
of the organism to dental conditions as shown in physical 
development, mental power, and the like. 

6. These things being true, it follows that the state of 
advancement reached in dentition is a good indication of the 
stage of progress which a child has reached in his total physi- 
cal development. The transitional features described there- 
fore take on an additional significance. 

Grozvth of the Skull. — The period of life under considera- 
tion is apparently transitional as regards the growth of the 
skull. In Ouain's Anatomy (70, p. 82) we read: 

"The skull grows rapidly during the first seven years of life. By 
that time, certain parts, including the circumference of the occipital 
foramen, the body of the sphenoid, the cribriform plate, and the petrous 
division of the temporal have attained their definitive size. The 
other regions also increase but little until the approach of puberty, 
when a second period of active growth begins, affecting especially 
the face and frontal portion of the cranium, with which is associated 
the expansion of the frontal and other air sinuses." 

These facts become the more interesting when we recall 
that cessation of growth in these portions occurs at just 
about the same time as the beginning of more rapid growth 



304 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

in parts of the face, as previously described, and as demon- 
strated by West (97) and by Rose (75). 

Grozvth of the Brain. — Data with regard to the size of 
the normal brain at different stages of development are 
meagre. Aside from this, there are many difficulties which 
arise from unavoidable inaccuracies in methods of sectioning 
and preparing specimens, and also from the fact that indi- 
vidual variations are great. Averages of brain weights are 
therefore of doubtful value. 

It is generally agreed that the early years are years of very 
rapid gain in brain weight. There are no data, however, to 
show beyond question that a distinct nodality occurs at the 
beginning of the later childhood period. Curves for brain 
weights at different ages can only be said to suggest that 
this is true. Pfister is reported to have found that the brain 
weight at the end of the sixth year is not infrequently equal 
to that of the adult (71, p. 342). This is also observable in 
the tabulation of brain weights collected by Vierordt (90, 
pp. 36-37). Donaldson, in his study of the brain was led to 
conclude, largely on the basis of the curve for brain weights 
collected by Vierordt, that, '\ . . .By the seventh year the 
encephalon has reached approximately its full weight, the sub- 
sequent increase being comparatively small . . ." (30, p. 104). 
We may say, therefore, not that brain weights show, but 
rather that they suggest a transition from rapid gain in gross 
weight to a different mode of development from the 'school 
age onward. This suggestion is strengthened by the fact that 
the rapid growth of the skull ceases at about the same time. 
Again, psychological investigations seem to show for this 
period a rapid development of muscular control, and the like, 
suggesting development along the line of better mner organi- 
zation rather than by means of mere addition of material. 

Development of the Eye. — Embryonically, the eye develops 
as a specialized portion of the brain. It is therefore interest- 
ing to note that there is some indication of its having attained 
approximately adult size at the same time with the brain. 
Stratz (86, a) has noted the relatively large size of the eye 
as compared to the small face of the child in the early years, 
due in part, of course, to the rather late development of the 
facial portions. The statement of Merkel would indicate that 
there is a further possible explanation. Without giving data, 
he says (55, Vol. i, p. 256) : " In connection with the de- 
velopment of the whole eye-ball, it occurs that the horizontal 
breadth of the iris is already reached in the sixth year of 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 305 

life." Parallel to this fact — provided data may be found to 
support it as fact, — there occurs at about the school en- 
trance age a transition in power to use the eye and also to 
control its movements. 

An important factor is the power to employ binocular 
vision. In this is involved the ability to " fuse " the slightly 
different images from the two eyes and interpret them as one 
object. This begins in the first few weeks of life, and accord- 
ing to Miss Sayer (82), is usually complete about the sixth 
to ninth year of life. In learning to overcome the difficulty, 
the child has a tendency to " squint," but overcomes it after 
learning to use the eyes properly. From defects of vision, 
however, he may develop a permanent " squint." This is 
easily cured by means of the amblioscope if taken before the 
age of six, but otherwise it develops, as does stammering, 
into a pathological condition that is very difficult to cure. The 
statement of Dr. Cornell (23, p. 243) with regard to this con- 
dition is in agreement with that of Miss Sayer. Again, while 
largely dependent upon central brain structure, there should 
be mentioned in this connection the lack of power to retain 
visual imagery in case of those persons who become blinded 
earlier than the fifth to seventh year (49). 

Here, again, phenomena which apparently involve both 
visual organs and visual brain centers would seem to suggest 
strongly that the closing years of earlier childhood constitute 
a time of change, both with respect to structural development 
and functioning. 

Larynx and Voice. — Vocal organs and vocal powers give 
evidence of a nodality of development at beginning of the 
later childhood period. Of the larynx Barth (6, p. 86) 
writes : 

"In the first two years of life the growth of the larynx is very 
slight. With the active use of speech in the following years the 
growth progresses more rapidly. It appears, however, to be limited 
more to the muscles that move the vocal cords. From the sixth to 
the fourteenth year of life the growth of the larynx is almost sta- 
tionary again, or, if it is present, is very slightly noticeable, strikingly 
and disproportionately less noticeable than the growth of the remain- 
ing organs of the body." 

Cunningham's Anatomy makes a similar statement (28, p. 
972) : 

" In the newly born child, the larynx, in comparison with the rest 

of the body, is somewhat large ( ) and it continues to grow 

slowly and uniformly up to the sixth year of childhood. At this 
period there is a cessation of growth, which persists until puberty 
is reached, and then a stage of active growth supervenes." 



3o6 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 



Gutzmann's diagram of the averages for normal children 
of both sexes up to the age of fifteen {2,7, p. 51) indicates 
a rapid widening of the range of voice, beginning at the age 
of seven. Differentiation of the sexes is also shown at this 
time, the range for girls being wider than that for boys from 
this age onward. The diagram is as follows. 



* 



Age: O 



i 



1-2 



i 



3-5 



St 



^^-6 



»--t5»--?5 



Z/^ 



9 



10 



12 •: 



11 



zn^rrz 



13 



14^ 



N euro -muscular Control. — Differences in the power to con- 
trol bodily organs indicate a transitional period at six or seven 
years. Speech development also gives such an indication. 
Apparently this period marks a stage of completion in speech 
coordinations, since infantile babble, if continued after this 
time, is usually considered pathological (22). Control of 
visual organs, as previously described, gives a similar indica- 
tion. Unless corrected before this period, " squint " becomes 
permanent. Vocal power, on the other hand, as indicated by 
the range within which pure tones can be sung, shows a rapid 
increase from this time on (37). The two sexes also show a 
difference in breadth of range from this period onward, at 
least up to the pubescent years. Bryan's tests of precision in 
finger movements (14) showed that in both the "up" and 
" down " writing movements almost half the gain between the 
ages of si'x and sixteen was made between the ages of six 
and eight years. Halleck has stated, " The vital time for 
motor training is before the age of eight " (40, p. 835). 

Pathological Conditions. — Some pathological conditions 
may be grouped together to show a relationship to this period 
of life. Stuttering, which differs somewhat from the infantile 
babble previously referred to, has been shown to be more 
prevalent at seven to eight years of age. Conradi (22) be- 
lieves there is a causal connection between this and dentition. 
Jastrow (49) found among some 200 persons in institutions 
for the blind that those who had lost the power of sight 
previous to the age five to seven years did not retain 
visual imagery in their dreams in after years. Those 
blinded later than the age of seven, on the other hand, did 
retain visual imagery. Clouston, in his " Neuroses of Devel- 
opment " (21^), long ago observed that the age of seven or 
eight is a time when many neuropathic conditions are liable to 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 307 

break out. In this connection again should be mentioned that 
" squint," also infantile babble are but natural when occur- 
ring previous to this age, while if lasting longer they seem 
to be so deeply grounded as to constitute pathological condi- 
tions. 

These are by no means proofs, nor is the list complete, yet 
the suggestion is strong that after this period of life the 
physical organization is somewhat different from that which 
precedes. 

Mental Development. — Adequate treatment of this topic 
would make this paper far too voluminous. We can touch 
it but briefly, stopping only for some general statements, 
chiefly concerning its relationship to our problem. 

Early years have long been recognized as a time of sensory 
training, shorter attention span, shorter memory span, etc., 
but no sharp transition has been clearly shown. Mental tests 
are not yet sufficiently refined to grade accurately small steps 
of advancement. Individual variations are too great. 

Though evidence to the contrary may be found, that there is 
a correlation of mental and physical development during 
school life has been indicated in a general way by such in- 
vestigations as those of Porter (67), Smedley (84), Ouirsfeld 
(72) and Crampton (26). Methods of grading mental ad- 
vancement with reference to stage of physical development 
rather than chronological age at this period, however, have 
yet to be worked out. There is needed here much further 
investigation, on the individual plan, for the purpose of find- 
ing the degree of mental advancement that may be expected 
in a pupil of either sex who has reached a given stage in his 
or her physical development. The question arises as to 
whether such investigation might not show a characteristic 
of mental development corresponding to the transitions in the 
physical. Facts of brain growth, neuro-muscular control and 
the like suggest that this might be true. 

Summary. — By way of summary we may generalize with 
regard to the preceding facts bearing on the question of 
nodality at the school entrance period as follows : 

1. Disturbances of growth in height and weight have been 
noticed at this period but their nature is imperfectly under- 
stood. 

2. Dentition shows distinctly a transition at this period, and 
because of close relationship to other phases of development 
suggests strongly that it is general in its nature. 

5. Both skull and brain show a change in growth rate at 
about this time of life. 



308 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

4. Growth of larynx and development of voice range indi- 
cate transition in these years. 

5. The statements of some authorities with regard to 
growth of the eye and control of its movements suggest nodal- 
ity in its development at this age. 

6. Phenomena of muscular control, also facts regarding 
pathological conditions, give evidence of a change in physical 
organization after this period. 

7. A clear-cut mental transition has not been shown, but 
tests have not related mental to physical stages of advance- 
ment. General correlations of mental and physical powers 
and facts regarding brain growth and muscular control sug- 
gest that tests relating these phases would indicate a transition 
here also. 

On the basis of these facts it appears that the question 
regarding a transitional stage of development at the begin- 
ning of later childhood should be answered in the affirmative. 
The time at which these phenomena occur is of course only ap- 
proximate, being based upon averages in most cases. The 
degree to which these changes are interdependent is also un- 
known. Whether they are all secondary to one basal, radi- 
cal change, as for example dentition, or whether they repre- 
sent a more general reorganization to which each is related 
cannot be stated. It seems probable that the latter is the 
case, although it is a problem that must be left open. It is 
certainly one that merits further investigation. 

Comparative Development of the Sexes. 

If, now, we give attention to the question of the compara- 
tive development of the two sexes at the school age, we are 
led to the consideration of a number of groups of data simi- 
lar to those of the preceding section. 

Occasional statements with regard to differences of the 
sexes at this early period of life have been made. Tyler (88, 
p. 139) thought girls of six begin to show signs of the precocity 
which characterizes later development. Rose mentioned dif- 
ferences of sex at time of second dentition {yy, p. 555). 
Stratz (86 a) thought sex differences in bodily form first be- 
come evident at the age of six, after which girls show more 
grace of curve, boys more of angularity and strength. For 
the most part, however, it has been taken for granted that the 
development of the two sexes is the same until some time 
after this period of life is passed. 

In an article published at a time w^hen this study was near 
completion, Dr. Boas (9) made some comparisons of develop- 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 309 

ment, particularly in dentition and ossification of the skeleton, 
which showed a greater advancement on the part of girls at 
this period. As he has stated, however, the number of data 
was limited, and the study rather of a preliminary nature. 
While his conclusions are partially correct, it may still be 
said that no extended comparison of facts has been made to 
decide the matter of comparative advancement of the physical 
development in the sexes at the beginning school period of 
life. It is our purpose here to attempt such a comparison. 

Height. — Comparison of absolute height at any given time 
in the early years does not show any cause for a differentia- 
tion of the sexes. The same is true of comparisons where 
added increments are reckoned as percentages of previously 
attained height. A question arises, however, as to whether 
this is an adequate method for getting at the actual attainment 
for a given age. At maturity the male is considerably larger 
than the female. Nor do they reach maturity at- the same 
time. If, then, our final comparison is to be one of unequals, 
comparisons previous to that time should not be on a basis 
of absolute equality, else erroneous conclusions will result. 
What we should ask is not, " Does the height of the boy equal 
that of the girl at a given age?" Rather should the question 
be, " What are the percentages of final, adult height reached 
in the two cases at a given age? " 

Comparison by such a method has been attempted. In a 
preliminary reckoning, taking Dr. Boas' averages for children 
of larger American cities, as given by Burk (17, Table H.), 
the average height of boys at 6.5 years is 69.88% of the ave- 
rage at 15.5 years, while of girls it is 70.35%. 

Results thus computated, on the basis of data from a num- 
ber of extended investigations, are given in Table D. Except 
in the last three cases, where the references are indicated, these 
are on the basis of the corrected averages given in Burk's 
"Table A" (17). These last three are not the corrected 
averages. Since adult heights could not be secured from the 
tables, the average at 17.5 years has been chosen as repre- 
senting post-pubescent height. 

Since girls are nearer adult height at the age of 17.5 years 
than boys of equal age, it is evident that they are at a dis- 
advantage in these comparisons. Yet in every case the indi- 
cation is that they have attained a greater percentage of their 
post-pubescent height at the age of 6.5 years than boys of the 
same age. Comparisons with averages of adult height would 
be more accurate, but it is plain that they would also show 
greater differences of the percentages, thus making the girls 
appear still more advanced, relatively. 



3IO 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 



TABLE D. 

Percentage of Post-pubescent Height Attained at 
School Entrance Period. 



Investigator 


A 




Com- 
pared 
to 


Percentage for 


"■a^ 


Boys 


Girls 


Bowditch (Boston) 

Porter (St. Louis) 

Peckham (Milwaukee) . . 

(Oakland) 

West (Worcester). . . 

Gilbert (New Haven) . 

Gilbert (Iowa) 

Key (Sweden) 

Anth. Com'n . . (England) .... 

Quetelet (Belgium) . . . . 

Pagliani (Turin) 

Hertel (Denmark) . . . 

' Smedley (Chicago) 

^ Lange (Germany) .... 

^Bobbitt (Phil. Is.) 


6-5 

< 


yrs. 
5 


i7-5/rs. 

16.5 yrs. 
17.5 yrs. 

17 


66.08 
66. 
66 . 10 
58.20 

66 .90 

67 .06 
65-98 
69 .40 
66 .46 
65.60 
64 .60 
68.11 
66 .99 
60 .38 
72.89 


70.03 
67 .60 

69 .60 

70 .80 
69.70 
70.70 
69.14 
70 .60 
68.60 
66.66 
65 .90 
70.40 
70.29 
69.31 
7«-33 



iSee (84). 



See (90, pp. lo-i i). 



See (12). 



As a matter of interest, comparison of average heights of 
feeble-minded in nineteen institutions, as given by Goddard 
(35), was made, using ages six and twenty. Percentage of 
twenty-year height reached at the earHer age was, for males, 
66.76, for females, 68.82. 

Weight. — As in case of height, data for the average at- 
tainments of weight have not indicated any differences in the 
sexes preceding the pubescent period of growth. Both Porter 
(66) and Burk (17) noted a slight superiority of boys during 
the first few school years. Applying the method of compari- 
sons just used in case of height, however, and using again 
the corrected averages from Burk's collection of data (17, 
Table E), we obtain the results presented in Table E. 

While there is slight lack of uniformity in these results, in 
general it holds true that there is shown a superiority of girls 
in the amount of post-pubescent weight attained at the ear- 
lier age. 

In case of both height and weight, therefore, the relative 
attainment of girls is shown to be slightly superior to that of 
boys at about the age of 6.5 years. 

Skeletal Development. — Radiographic studies have shown 
that ossification of the skeleton proceeds more rapidly in girls 
than in boys during the early years. This is especially notice- 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 3II 

TABLE E. 

Percentage of Post-pubescent Weight Attained at 
School Entrance Period. 





Age 


Com- 
pared 
to 


Percentage for 




Boys 


Girls 


Bowditch (Boston) 

Porter (St. Louis) .... 

(Oakland). .. . 

Peckham (Milwaukee) . . 

West (Worcester). . . 

Gilbert (New Haven) . 

Gilbert (Iowa) 

Key (Sweden) 

Hertel (Denmark) . . . 

Erismann (Moskow) .... 

Pagliani (Turin) 

Anth. Com'n . .(England) .... 
_Misawa (Japan) 


6.5 yrs. 

7-5 yrs. 
6.5 yrs. 


17.5 yrs. 

16.5 yrs. 
ly.S^^yrs. 


35-45 
35-58 
36.14 

34-35 
34-64 
36.00 
32.82 
39-60 
39-64 
34.83 
31.66 

33-91 
34-61 


37-48 
35-94 
38-99 
38.04 
38.00 
38.96 
34-38 
39-53 
39-23 
42.37 
34.57 
36.10 

37-14 



able in the carpal bones of the wrists and the epiphyses of the 
joints. Dr. Rotch makes this statement, but gives few data 
(80, p. 416). Pryor's studies, however, give data by which 
this seems to be clearly indicated (69), though their number is 
limited. He quotes a conclusion from a previous paper by 
himself as follows (69, p. 3) : " The bones of the female os- 
sify in advance of the male. This is measured first by days, 
then months, then years." 

Choosing the trapesoid bone of the wrist as an example, 
we may note that he finds its time for ossification to be be- 
tween the fourth and fifth year in the female, between the 
fifth and sixth year in the male (69). 

Dentition. — Differences in the time of eruption of the 
teeth should again be emphasized at this point. Greater ra- 
pidity in the eruption of the teeth of girls was shown in case 
of each of the investigations referred to, beginning with the 
first molars and continuing up to the time of appearance of 
canines and second molars. The difference is by no means 
as great, however, at the first molar stage as Boas found 
(9, p. 815) from his limited collection of data. Rose's 
averages show the difference in time of first molars to be as 
small as one to two months. It should be emphasized again 
that the difference in eruption time of the teeth grows pro- 
gressively greater with advancement of dentition. By the time 
the second molars appear, the difference in time between the 



312 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

two sexes approximates the difference in time between their 
attainment of pubescence. 

Groivth of the Brain. — The limited number of data ren- 
ders comparisons of brain weights for the two sexes very 
difficuh. Only general indications may be noted. Curves 
constructed on the basis of Vierordt's data (30, p. 105) seem 
to indicate an earlier attainment of adult brain weight in 
females. This can be said to be little more than an indica- 
tion, however, on account of the difficulties of method for- 
merly referred to and the great variability in brain weights. 

N euro-Muscular Development. — The probability indicated 
by brain weights is in correspondence with that indicated by 
facts of muscular control. Hancock found in his swaying 
tests that girls were more steady in the early years than boys 
(41). Automatograph tests showed better lateral control of 
the arm, and tremograph tests showed greater control of fin- 
ger movements among girls also. Observations of less defi- 
nite tests again showed the superiority of girls in control of 
movements. 

Bryan's tapping tests seem to be alone in their showing 
of better control on the part of boys. He says (14, p. 173) 
that differences are slight, but that within the narrow limits 
indicated there is a slight superiority of boys over girls. 

Strength tests were compared by Burk (17) by a method 
similar to the one we have used for height and weight. From 
the data of Porter, Roberts and Gilbert he found percentages 
indicating that boys had attained 1/5 their sixteen-year 
strength at the age of six years, 1/4 from six to eleven. 
Girls had gained a greater percentage at six, and from this 
on their acquirement was m.ore rapid than that of boys. 

Gesell noted that boys as a class show greater tendency 
toward uncoordinated writing as early as the first grade and 
up through the high school (33). 

In this connection should be mentioned again that, begin- 
ning with the age of seven, the range within which pure tones 
can be sung is wider for girls than for boys. 

Stuttering, which begins most often in the early years, has 
been found in a number of investigations to be more preva- 
lent among boys (22, p. 361). Various ratios for the sexes 
have been reported. Conradi reports also that girls learn to 
talk earlier than boys (22, p. 363). 

With the exception of the tapping tests, all the indications 
of power of control here enumerated show superiority in girls. 

Summary. — On the basis of the data here presented it 
seems fair "to conclude that the physical development of girls 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 313 

is relatively more advanced than that of boys at the age of 
five or six or thereabouts. On the average they have then 
attained a greater percentage of their post-pubescent height, 
a greater percentage of their post-pubescent weight, their 
skeletal development is more advanced, and their dentition 
has progressed further. Aside from this there is a strong 
suggestion that a greater percentage of adult brain weight 
has been attained by them, and this is supported by the fact 
that most data available show a more advanced power of 
neuromuscular control. How great the difference in general 
physical development is a matter to be determined by fur- 
ther investigation. 

Discussion, Pedagogical Suggestions, and Summary 

So far, the aim has been to find solutions for our two main 
problems. For the first we may say that, while not proved, 
a great mass of data indicate a transition in physical develop- 
ment at the period of usual school entrance. Regarding the 
second we may say that greater advancement in the physical 
development of girls at this time is pretty clearly shown. 

The solution or partial solution of these two problems sug- 
gests a number of others. If this is a transitional period, 
what is its fundamental nature? Is the transition general or 
due to a single factor, as dentition? That it is the former 
seems to be the case, but it is still an open problem. In case 
the transition is not of a general, fundamental nature, then 
a whole series of problems regarding the relationship of these 
several transitional phenomena arise. For example, is ra- 
pidity of dentition to be correlated with rapidity of skeletal 
ossification, as Holt (45) has stated is the case in infancy? 
Are disturbances of growth in height and weight noted at 
this period due to conditions of dentition or do they occur 
regardless of it? 

The correlation of mental with physical development at 
this period is a problem which those working with mental 
tests cannot afford to neglect. Granted a degree of physical 
and mental correlation, and that this period is a transitional 
one for physical development, then the whole question of 
qualification for school entrance is thrown open anew. The 
problem is still further complicated by the fact of great 
variability shown in the developmental factors at this time. 

In view of their close relationship to other phases of physi- 
cal development, and in the absence of definite methods of 
grading, the question arises as to whether the time of ap- 
pearance of the first molars could not be cited as a point 
before which school duties should not be imposed. 



314 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

The differences of the sexes at this period also suggest 
some important problems. Recalling that the female reaches 
maturity some three years earlier than the male — or nearly so 
— and that she reaches the pubescent stage almost two years 
earlier, on the average, the fact that she has progressed fur- 
ther at the school entrance age is to be expected. The ques- 
tion arises here, however, as to how early the differentiation 
of the sexes actually begins. Since differences in the averages 
of absolute measurements are noticeable at birth, and in view 
of the popular opinion that the prenatal period is shorter for 
females than for males, one is tempted to raise the question 
as to whether differentiation does not actually begin before 
birth. 

The problem of the amount of difference between the sexes 
comes up, and also the further one of working out a method 
sufficiently refined to measure them. The question as to 
what this difference signifies for the pedagogy of this period 
of life is an extremely important one. 

The preceding facts and conclusions form the basis for 
some further conclusions and suggestions for the hygiene and 
pedagogy of the early years of childhood. 

We have shown that boys and girls of equal age are not 
equally advanced physically at the school entrance period of 
life. We have presented a mass of evidence in support of 
the conclusion that this is a transitional period in the physical 
development, referring to the great individual variability, as 
indicated by dentition, skeletal development, etc. Associat- 
ing these facts with the indications of a correlation between 
mental and physical development, the need of a physiologi- 
cal grading for entrance to school becomes strikingly evident. 
Granted a proper grading for entrance on this basis, the grief 
and the expense of " repeaters " up through the grades would 
be tremendously lessened. School entrance should be on the 
basis of the fitness of the individual, not on the basis merely 
of his chronological age. 

Again, the rapid growth, the ease with which the delicate 
balance of the organism may be overthrown, the lasting detri- 
mental results following the wrong " inclination of the twig," 
all suggest that the thing of supreme importance in these 
early years is rather health and development than formal 
school work. The paramount importance of habits of health is 
shown over and over again in case of the teeth. Lack of the 
habit of cleanliness of the teeth is followed by caries, loss 
of bicuspids or all important first molars, with probably ill- 
fitting permanent dentures, deformed facial features and in- 
jury to health. Habits of thumb-sucking, mouth-breathing, 



PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 315 

and the like, may cause malocclusion and abnormal growth 
of jaws and related facial parts. Good permanent tooth 
crowns are largely dependent upon fresh air, exercise and 
good nourishment throughout the first five or six years of 
life. Attention to all these things should be first until after 
the organization of the childish body is more nearly complete. 

The eyes are unfit for close visual work until after the 
transitional period. 

Adenoids left uncared for in these early years are liable 
to cause disturbances of development. According to Yearsley 
(104) the time to have them removed is after six months 
and before six years of age. 

Enlargements of the tonsils, with decreased power to resist 
invasions of micro-organisms, accompanies eruption of the 
first molars, in many cases (100, p. 13). Until after this 
time, no child should be confined to the school room where 
his chances of exposure to infectious disease germs are in- 
creased. 

In view of all these things, this survey would be worth 
while, even though it did no other thing, could it portray in 
its true light the importance of all the years of earlier child- 
hood for the normal, healthy physical development of the 
child. 

From a different viewpoint another suggestion is in place. 
Could " types " be agreed upon for use in comparisons of 
stature, and like physical characteristics, similar to these used 
in anthropometry, much more accurate knowledge of develop- 
ment might be gained. Grouping of material according to 
types, combined with comparisons of relative advancement, 
such as we have used above, should lead to more satisfactory 
results in indicating stages of development. 



Final Summary. 

The main conclusions to which the facts presented in this 
thesis point are : 

1. That there is a mass of evidence indicating a transition 
in the physical development of the child at the period of usual 
school entrance. 

2. That there is evidence to show that girls are on the 
average more advanced in their physical development at this 
period. 

5. That requirements for entrance to school based on stage 
of progress in physiological development, or physiological 
age, would be far superior to a requirement taking account of 
chronological age only. 



3l6 PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 

4. That in the appHcation of physical measurements for 
the purpose of finding degree of progress in physical develop- 
ment, a method indicating the percentage of adult size at- 
tained at a given age is superior to a method comparing 
absolute data directly. 

5. That the hygiene and pedagogy of this period are of 
prime importance for the future development and welfare 
of the individual. 



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PHYSIOLOGICAL AGE AND SCHOOL ENTRANCE 32I 

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